ACK/NACK Codebook Size Determination in Inter-Band TDD Carrier Aggregation
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Solution Overview
Problem
Inter-band TDD carrier aggregation with different UL/DL configurations on different bands leads to complexities in HARQ feedback timing, causing misunderstandings in ACK/NACK codebook size determination between the eNB and UE, which can degrade DL performance.
Innovation Solution
The proposed solution involves defining two types of DL subframes (type 1 and type 2) and adjusting the UL DAI indication scheme to accurately determine the ACK/NACK codebook size, ensuring correct feedback transmission and avoiding misunderstandings by considering the maximum number of scheduled type 1 and type 2 DL subframes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If inter-band TDD carrier aggregation with different UL/DL configurations is implemented, then bandwidth and communication flexibility are improved, but HARQ feedback timing complexity and codebook size determination errors increase
Solution Approach 1:
The patent segments DL subframes into two types: type 1 subframes (where all serving cells can be scheduled) and type 2 subframes (where not all serving cells can be scheduled due to UL/DL configuration constraints). This segmentation allows the system to handle different subframe types with appropriate scheduling rules, resolving the timing complexity while maintaining carrier aggregation flexibility.
Solution Approach 2:
The patent changes the parameter interpretation of UL DAI by defining it to indicate the maximum number of type 1 DL subframes plus the maximum number of type 2 DL subframes. This parameter change enables accurate codebook size determination by aligning the UL DAI value with the actual scheduling capacity across different subframe types, eliminating codebook size mismatches between eNB and UE.
2Measurement precision
If UL DAI indication scheme is adjusted to account for type 1 and type 2 DL subframes, then ACK/NACK codebook size accuracy is improved, but signaling and processing overhead increase
Solution Approach 1:
The patent makes the UL DAI parameter serve multiple functions: it simultaneously indicates the maximum number of type 1 DL subframes and the maximum number of type 2 DL subframes. This multi-functionality allows accurate codebook size determination without requiring separate signaling fields for each subframe type, thus avoiding additional signaling overhead while maintaining precision.
Data Source
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AI summary
A method comprising: using first information and second information to determine a code book size, said first information comprising information for at least one first subframe of at least one cell for which feedback information is to be provided, said at least one first subframe is prior to subframe n and second information for at least one second subframe of at least one cell for which feedback information is to be provided, said at least one second subframe being after said subframe n ; and using said code book size for providing feedback information.